(1) Field of the Invention
The present invention relates to a bus system in which a plurality of device units are connectible on the same bus, like a peripheral component interconnect (PCI) bus system employed in a storage system. The invention also relates to a bus system design method suitable for designing that bus system, and a device unit connectible to that bus system being in an active state.
(2) Description of Related Art
For example, a storage system is equipped with a plurality of disk units (magnetic disk units, physical device units), and is used for writing the data from a server (host) to these disk units in response to access from the server, or reading out the data requested by the server from the disk units and transmitting that data. Such a storage system includes a host interface module, which transmits data to the server through a fiber channel interface bus.
The host interface module is connected to a PCI bridge module through an interface bus such as a PCI bus and transmits data to a disk interface module, management module, etc., connected to the PCI module through the PCI bus.
The host interface module is also constructed as a single unit by mounting a central processing unit (CPU), memory, and other devices on a printed-circuit board (PCB). If the thus-constructed host interface module is fitted or inserted in a mother board having a PCI bus, the devices constituting the host interface module are communicably connected on the PCI bus. In this way, a storage system with the required number of host interface modules can be easily constructed.
If the host interface module is connected on the PCI bus of the mother board being active (active insertion), noise occurs on the PCI bus because of that active connection and has an adverse influence on the operation of other host interface modules connected on the PCI bus and operation of various devices constituting the mother board.
To prevent the adverse influence due to active insertion of host interface modules, operation of the PCI bus is generally stopped. For example, Japanese Laid-Open Patent Publication No. HEI 7-253834 discloses a module insertion control device that controls noise propagation by connecting or disconnecting some of switches during active connection and disconnection, to prevent modules from failing or operating incorrectly.
However, if the bus operation of the PCI bus is stopped in order to insert host interface modules, data transmission through the PCI bus cannot be performed during the stoppage and therefore the data transmission efficiency is reduced. Also, since a variety of operations for monitoring whether or not host interface modules are inserted in the PCI bus and stopping the PCI bus are needed, system control is frequently performed and system design efficiency is reduced.
Furthermore, a dedicated control device for active insertion (active connection) adds to manufacturing costs and results in an increase in device size.